[MR2] MKII Strange Noise

[Bryan Kohart]

I was driving down the interstate the other night, and the engine started making a new noise.  I had no idea what it might be, so I had the car towed home and haven't driven it since.  I'm not really sure how to describe it, so I made a youtube video:  http://www.youtube.com/watch?v=KWy0BiCZeqM&feature=youtu.be I'm having trouble locating the source of the noise, so any tips are appreciated.  Some info that might be useful:  I bought the shortblock new from Toyota about 6,000 miles ago.  At the same time, I had the head serviced (cleaned, resurfaced, valve job) and installed a fresh ATS CT27.  Not counting the Exedy OE spec clutch and the CT27, everything on this engine is OEM.  The tranny has somewhere around 110k miles and makes a whirling noise in 4th and 5th gear, but this new noise doesn't seem to be tranny related.  I pulled the valve cover and plugs to look at the top-end, but I didn't see anything obviously loose, broken, or contaminated.  The engine didn't seem to skip a beat when this noise started, and it will only occur if I get the RPMs up.  The noise happens more frequently if I quickly rev the car, and it doesn't happen at all if I just let it idle.  I was cruising in 5th gear on the highway @ 75 MPH when this noise started suddenly.  You'll notice in the video that the noise builds up (almost sounds like really bad pinging) and then makes a loud "zzzziiiiiiipppp" sound at around 25 seconds.  Any ideas on where to start? Bryan